JP2005501467A - Method and apparatus for W-CDAM handoff search - Google Patents

Abstract

Methods and apparatus for W-CDAM handoff search United States Patent Application 20070228305 Kind Code: A1 Techniques for improved handoff search in asynchronous systems such as W-CDMA are disclosed. In one aspect, if the neighbor code list is known, a two-step search procedure is used. In a first step, the received signal is correlated by a slot timing code to locate one or more pilots and their associated slot boundaries. In the second step, the received signal is correlated by each of the code lists at the slot boundaries identified by the pilot in the first step to identify the pilot code and the frame timing associated with each pilot. Various aspects of the invention are also shown. These aspects have the advantage of reduced search time resulting in increased acquisition speed, higher quality signal transmission, increased data throughput, reduced power, and improved overall system capacity.

Description

【Technical field】
[0001]
The present invention relates generally to communication, and more specifically to a new and improved method and apparatus for W-CDMA handoff searching.
[Background]
[0002]
Wireless communication systems are widely used to provide various types of communication such as voice and data. These systems may be based on code division multiple access (CDMA), time division multiple access (TDMA), or other modulation techniques. CDMA systems offer certain advantages over other types of systems, including increased system capacity.
[0003]
The CDMA system consists of (1) “TIA / EIA-95-B mobile station-base station compatibility standard for dual-mode wideband spread spectrum cellular systems” (IS-95 standard) and (2) “3rd generation partnership project ( 3rd Generation Partnership Project) ”(3GPP) and includes a set of document numbers 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 The standard (W-CDMA standard) embodied in the document and (3) C.S0002 for a cdma2000 spread spectrum system provided by a consortium called “3rd Generation Partnership Project 2” (3GPP2) -C.S0002-A Physical Layer Standard for c dma2000 Spread Spectrum Systems), "C.S0005-A Upper Layer (Layer 3) Signaling Standard for cdma2000 Spread Spectrum Systems", and C. S0024 cdma2000 High Rate Packet Data Air Interface Specification (cdma2000 standard) and (4) one or more CDMA standards such as other standards to support It may be designed to.
[0004]
Pseudo random noise (PN) sequences are commonly used in CDMA systems to spread transmitted data including transmitted pilot signals. The time required to transmit the signal value of the PN sequence is known as the chip, and the rate at which the chip changes is known as the chip rate. A CDMA receiver generally uses a rake receiver. A rake receiver typically receives one or more searchers for locating direct and multipath pilots from one or more base stations and information signals from these base stations. And two or more multipath demodulators (finger) for combining.
[0005]
The requirement that the receiver must adjust its PN sequence to that of the base station is inherent in the design of direct sequence CDMA systems. For example, in IS-95, each base station / subscriber unit uses the exact same PN sequence. The base station identifies itself from other base stations by inserting a unique time offset in its PN sequence generation (all base stations are offset by an integer multiple of 64 chips). A subscriber unit communicates with a base station by assigning at least one finger to the base station. The assigned finger must insert an appropriate offset into its PN sequence to communicate with its base station. The IS-95 receiver uses one or more searchers to locate pilot signal offsets, thereby using those offsets for receiving finger assignments. Since the IS-95 system uses a single set of in-phase (I) and quadrature (Q) PN sequences, one method of pilot positioning is internally generated until one or more pilot signals are positioned. Simply searching the entire PN space by correlating the resulting PN sequence with different offset hypotheses.
[0006]
Other systems, such as W-CDMA systems, differentiate base stations that each use a unique PN code, known as the primary scrambling code. The W-CDMA standard defines two Gold code sequences for scrambling the downlink, one for in-phase component (I) and one for quadrature (Q) It is for. Both I and Q PN sequences are broadcast via cells without data modulation. This broadcast is called a common pilot channel (CPICH). The generated PN sequence is cut to a length of 38,400 chips. The period of 38,400 chips is called a radio frame. Each radio frame is divided into 15 equal sections called slots.
[0007]
It is possible to search for W-CDMA base stations in the manner described above for the IS-95 system. That is, the entire PN space is searchable by offset (38,400 of them) for each of the 512 primary codes. However, this is not practical because of the excessive time that such a search takes. Instead, the W-CDMA standard calls the base station to transmit two additional synchronization channels and a primary and secondary synchronization channel to assist in the efficient search for subscriber units. As a result, the W-CDMA search can be performed in three steps and is described in more detail below.
[0008]
For initial acquisition, the three-step W-CDMA search provides a significant performance increase in terms of reducing search time for the impractical alternative of searching the entire PN space for each scrambling code. If the primary scrambling code of the neighboring base station is known, the handoff search can be successfully performed using either of two methods, each identified in more detail below, It shows certain drawbacks regarding search time.
[0009]
Search time is an important criterion in judging the quality of a CDMA system. A reduction in search time means that searches can be performed more frequently. Thus, the subscriber unit can often send and receive good signals with reduced transmission power by both the base station and the subscriber unit by locating and accessing the best available cell more frequently. This in turn increases the capacity of the CDMA system (with respect to either increasing users or support for higher transmission rates, or both).
[0010]
Reduced search time is also advantageous when the subscriber unit is in idle mode. In idle mode, the subscriber unit is not actively transmitting or receiving voice or data, but is regularly monitoring the system. In idle mode, the subscriber unit may remain in a low power state when not monitoring. By shortening the search time, the subscriber unit can reduce the monitoring time and increase the low power state time, thereby reducing power consumption and increasing standby time.
[0011]
The benefits of reduced search time are obvious, and several problems associated with searching in asynchronous systems such as W-CDMA, including handoff search, have been highlighted. Thus, there is a need in the art for improved search techniques for asynchronous systems, including handoff search.
DISCLOSURE OF THE INVENTION
[0012]
[Overview]
The embodiments disclosed herein illustrate the need for improved handoff search in asynchronous systems such as W-CDMA. In one aspect, a two-step search procedure is used when a list of neighbor codes is known. In the first step, the received signal is correlated by a slot timing code to locate one or more pilots and their associated slot boundaries. In the second step, the received signal is correlated by each of the code lists at the slot boundaries identified by the pilot in the first step to identify the pilot code and the frame timing associated with each pilot. Various other aspects of the invention are also shown. These aspects have the advantage of reduced search times resulting in increased acquisition speed, higher quality signal transmission, increased data throughput, reduced power, and improved overall system capacity.
[0013]
The present invention provides methods and system elements that implement various aspects, embodiments, and features of the invention, as described in more detail below.
[0014]
The features, nature, and advantages of the present invention will become more apparent from the following detailed description, taken in conjunction with the drawings. Throughout the drawings, the same reference numerals indicate the same parts.
[0015]
[Detailed description]
FIG. 1 is an illustration of a wireless communication system 100 that supports a large number of users and can implement various aspects of the invention. System 100 may be designed to support one or more CDMA standards and / or designs (eg, W-CDMA standard, IS-95 standard, Cdma2000 standard, HDR specification). Briefly, the system 100 is shown to include three base stations 104 that are in communication with two subscriber units 106. Base stations and their coverage areas are often collectively referred to as “cells”. In an IS-95 system, a cell may include one or more sectors. In the W-CDMA specification, each sector of the base station and the coverage area of the sector are referred to as a cell. As used herein, the term base station can be used interchangeably with the term access point. The term subscriber unit may be used interchangeably with the terms user equipment (UE), mobile station, subscriber station, access terminal, remote terminal, or other corresponding terms known in the art. The term mobile station includes fixed wireless applications.
[0016]
According to the implemented CDMA system, each subscriber unit 106 may communicate with one (or possibly multiple) base stations 104 on the forward link at a given moment, and the subscriber unit is in soft handoff. Or may communicate with one or more base stations on the reverse link. The forward link (ie, downlink) refers to transmission from the base station to the subscriber unit, and the reverse link (ie, uplink) refers to transmission from the subscriber unit to the base station.
[0017]
Specifically, the examples used in describing the present invention are base stations as signal transmitters and subscriber units as receivers and acquirers of those signals, ie signals on the forward link. Those skilled in the art will appreciate that base stations as well as subscriber units are provided for transmitting the data described herein, and that aspects of the invention apply to these situations as well. The term “exemplary” is used herein generically to mean “is an example, instance, or illustration”. Any embodiment described herein as "exemplary" is not necessarily configured as preferred or advantageous over other embodiments.
[0018]
Recall that a W-CDMA search can be performed using a three-step procedure. In step 1, the subscriber unit searches for a primary synchronization code (PSC), which is a component of the primary synchronization channel. PSC is a fixed 256 chip sequence that is transmitted between the first 256 chips of each 2,560 chip slot. The PSC is the same in every cell of the system. The PSC is useful for detecting the presence of a base station, and once acquired, slot timing is also acquired.
[0019]
In step 2, the subscriber unit retrieves the secondary synchronization code (SSC) that forms the secondary synchronization channel. There are 16 256-chip SSCs. The base station transmits 15 SSCs per frame (one SSC for each slot). There are 64 unique sequences of 15 SSCs, each sequence associated with one of the 64 scrambling code groups. Each base station transmits one SSC with a PSC in the first 256 chips of each slot (each of the 16 SSCs and the PSC are orthogonal). A set of 64 SSC sequences are selected to be comma free, ie any sequence is either a cyclic shift of another sequence, or any non-obvious one of its own Not equal to circular shift. Because of this nature, when a subscriber unit determines the sequence of SSCs transmitted in any 15 consecutive slots, it can determine both the frame timing and which of the 64 SSC sequences were transmitted. The scrambling code group to which the base station belongs can be identified. Since each scrambling code group has 8 codes, the number of candidates is reduced to 8.
[0020]
In step 3, the eight scrambling code candidates identified in step 2 must be searched to determine which is the correct code. This is performed by accumulating energy for multiple chips, performing a chip-by-chip correlation similar to the process described for IS-95 until a decision is made.
[0021]
Once the three-step search procedure has been completed and the base station has been acquired, the search task is still in progress. For example, neighboring base stations must be searched periodically to determine which, if any, is suitable for handoff. Already acquired base stations can provide a list of potentially accessible base stations, known as a neighbor list. Furthermore, the primary scrambling code of the base station in the neighbor list can be identified. That is, in the synchronization system, the reference with which the frame timing of the base station is synchronized in a system that performs adjacent search such as IS-95 and cdma2000 is very fast. This is because only a small window around the known frame boundary of each base station needs to be searched. However, in asynchronous systems such as W-CDMA, knowledge of neighbor lists and associated scrambling codes is not sufficient because the frame timing is unknown. A search still has to be performed to find asynchronous neighbor base stations. While searching for neighboring base stations while one or more base stations have already been acquired, one of the purposes of such searching is referred to herein as handoff searching because it facilitates handoff. The However, the term handoff search is not limited to situations where a handoff actually occurs.
[0022]
Two straightforward procedures for obtaining the frame timing of neighboring base stations include those referred to above. One procedure is to search the entire space of 38,400 chips for each scrambling code. For each hypothesis, the subscriber unit needs to integrate a certain number of chips in order to increase the likelihood of detection by reducing the average of the noise. Although impractical for initial acquisition, this method is useful when the number of scrambling codes as contained in the neighbor list is relatively small.
[0023]
The second method is to execute the above three-step search procedure. First, slot timing is obtained by searching the PSC. Secondly, the frame timing is obtained by searching the SSC as well as narrowing the scrambling code to a maximum of one of the eight hypotheses. In some cases, because the neighbor list is relatively small and therefore the number of potential scrambling codes is a subset of the total number of scrambling codes, SSC learning identifies which scrambling codes are being transmitted. Enough to do. Alternatively, at least one set of hypotheses may be reduced from the eight identified by the SSC sequence. Third, for each remaining hypothesis, the subscriber unit searches for a scrambling code in a small window around the frame boundary identified in the second step. Each step search requires the subscriber unit to integrate a certain number of chips to lower the noise average and increase the likelihood of detection.
[0024]
There are certain drawbacks to using either of the above two methods, which affects the total search time required for handoff search. Since the first method searches for 38,400 hypotheses, the chance of false detection due to noise increases. As described above, to address this, the subscriber unit integrates multiple chips to achieve the desired level of likelihood. This type of integration may require a neighbor search containing multiple frames. Furthermore, in handoff searches, generally only a few strongest neighbors are desirable. However, the use of the first method requires a search of the entire neighbor list to detect a few strongest cells. That is, the search time is linearly scaled by the total number of adjacent cells, not the strongest number of adjacent cells.
[0025]
The second method does not have the disadvantage of requiring a full neighbor list search to identify a small number of strong candidates. This is because the strongest PSC received in step 1 corresponds to the strongest candidate, so only a few strong candidates need to be searched in subsequent steps 2 and 3. However, recall that PSC and SSC are only transmitted between the first 256 chips of the 2,560 chip slot. Thus, in both steps 1 and 2, in order to consolidate multiple chips, the subscriber unit must wait for 2560 chips for every 256 chips to be merged. Furthermore, the primary and secondary synchronization channels are generally transmitted with lower strength than the primary scrambling code and are not orthogonal to it. These additional factors increase the time required for integration to achieve the desired performance level. Step 2 of identifying the SSC needs to be repeated for more than one slot hypothesis, returning to step 1, which is more susceptible to increased integration time in order to increase the total handoff search time.
[0026]
Various embodiments of the present invention combine aspects of the two search methods described above to perform a handoff search that avoids the disadvantages of using only one of the methods. FIG. 2 shows a flowchart of one such embodiment method for performing a handoff search. In block 210, the subscriber unit receives a primary scrambling code for an adjacent base station. The next blocks 220 and 230 define a two-step process for retrieving a known primary scrambling code, regardless of how the subscriber unit knows the code. Although the following embodiments are described with respect to a W-CDMA system, the principles of the present invention are such that the code for identifying slot timing and the start of the frame timing correspond to one of the slots in the frame. Applies equally to any possible system that employs a pilot code.
[0027]
The first step shown in block 220 consists of performing step 1 of the three-step search process described above. By searching the PSC, the slot timing of a few strongest cells can be obtained. Those cells that are very weak to consider in the process are eliminated. Performing this step avoids the need to perform a full search of the entire neighbor list if only a subset containing a few strongest cells is desired. After completion of this step, the subscriber unit will know the pilot slot timing of multiple candidate base stations. Since there are 15 slots in each frame, knowing the slot timing reduces the frame timing uncertainty for each pilot's 15 frame hypothesis.
[0028]
The second step shown in block 230 is to search each pilot hypothesis by testing each of the 15 slots using each of the codes in the neighbor list. Other codes (corresponding to weak cells or unreceived cells) may also be in the list, but the neighbor list is most likely to contain the primary scrambling code of the candidate base station pilot. For each code in the list, a small window is displayed for each slot boundary identified in the first step until a frame boundary is detected (or 15 slots have been tested and no code is detected in the pilot). Search around. The process is repeated until all pilot hypotheses (ie, base station candidates) in the subset detected in step 1 are identified by the primary scrambling code and the acquired frame timing.
[0029]
If the signal detected in step 1 is not from the neighbor list (or from a list of known base stations for search) but from the base station, the subscriber unit is one of a number of steps. Can be taken. The subscriber unit can ignore it because the base station is not on the list. Alternatively, it may continue through the last two steps of the above three-step search process until the base station is identified. The subscriber unit may send a message to the base station that it is already in communication and update the neighbor list with new candidates.
[0030]
FIG. 3 shows an embodiment of step 220 described above in FIG. Recall that step 220 is the first step in a two-step search process for locating neighboring pilots if the list of potential neighboring pilots and their corresponding codes are known. In step 310, incoming I and Q samples (eg, received from an RF down-conversion block such as block 620 shown in FIG. 6 and described in detail below) are correlated by the PSC for a period M. M may be defined as any time value, but a convenient choice would be M chips, M slots, or M frames. Because the various pilots being searched are asynchronous, it is desirable to search for each offset in one entire slot containing 2560 chips in order to detect all strongest candidates. In general, the search is performed in half-chip increments to account for chip alignment uncertainty, and the total number of hypotheses to be tested in a slot is twice the number of chips, ie 5,120. By selecting a relatively large value of M, the increased search time trade-off provides a more accurate energy measurement of the various hypotheses. Various means for correlating sequences such as PSC with incoming I and Q samples are known in the art, and one embodiment operable by the steps shown in FIG. 3 is detailed below with respect to FIG. The Techniques for using multiple correlators in parallel to reduce search time are also known in the art.
[0031]
In step 320, a number of strongest pilots J are located from the correlation result of step 310. As described above with reference to FIG. 2, it is advantageous to use search resources, including associated hardware and search time, for the strongest pilot available to the subscriber unit. One alternative is to fix J to a set amount and detect only the J highest pilots (and use all available pilots if fewer than J pilots are positioned) The result is to classify. Another alternative is to use a minimum energy threshold and set J to match the total number of pilots that meet or exceed that threshold. Yet another alternative is to change the minimum threshold according to the energy and / or number of pilots that are actually positioned. The positioned J pilots are used in step 230, which is the second step of the above two-step search process.
[0032]
FIG. 4 shows an embodiment of step 230 described above in FIG. Recall that step 230 is the second step in the two-step search process for locating neighboring pilots if the list of potential neighboring pilots and their corresponding codes are known. In FIG. 4, the four steps 410, 420, 430, and 440 correspond to four nested loops. A step that is nested in another step is shown as a box that is placed in an outer box corresponding to the other step.
[0033]
In step 410, each pilot j of the J strongest pilots determined in the first step 230 of the two-step search process is tested, and one or more of the codes corresponding to the base stations in the neighbor list are pilot j. It is determined whether or not it has been transmitted. In general, since adjacent base stations are asynchronous, only one base station may be detected by pilot j. However, two neighboring base stations may be temporarily synchronized, so that the designer of an embodiment may desire more than one pilot code search for each pilot j being positioned. Alternatively, if the likelihood of the event occurring is low, once a single base station is associated with pilot j, the designer may end testing for it. Details of both alternatives above are provided below in the embodiment described in FIG.
[0034]
Step 420 is nested within step 410. For each code k of up to K components in the neighbor list, a test is performed to determine whether code k is present in pilot j. To account for the situation where two or more pilots are temporarily synchronized with other base stations, all K tests may be performed on a single pilot j. In a somewhat powerful deployment of this embodiment, step 420 is applicable for each code k on each pilot j. However, if it is detected that the code k is present on the pilot j that has already been tested, each base station transmits a unique pilot, so that the code needs to be tested against subsequent pilots. Absent. Considering this in the deployment, the number K is reduced for the next round of step 420 since one or more codes k are associated with one or more pilots j, reducing the required search time.
[0035]
In each round of step 420, code k is tested for pilot j. If the code is not positioned at pilot j after all tests of K neighbor codes, the pilot does not correspond to one of the codes in the neighbor list. The subscriber unit can handle this situation in a number of ways. One way is to simply ignore pilot j and proceed to the next pilot test in step 410. Alternatively, a conventional three-step WCDMA search may be performed to determine which base station pilot j corresponds to, and the information is relayed to the system to locate the new base station in the neighbor list. May be added to Depending on the possibilities, any of the above alternatives may be selected by the system designer in a particular system deployment of subscriber units accessing neighboring base stations not included in the neighbor list.
[0036]
Step 430 is nested within step 420. Recall that positioning each pilot j of the J strongest pilots also determines the slot timing of that pilot. In step 230, where step 430 is a substep, the frame timing is also determined as the code k associated with each pilot. Thus, each slot i of up to 15 slots must be tested for each code k. Note that the 15 slots tested are the maximum required. If code k is positioned before 15 slots are tested, the code and frame timing has already been determined. Thus, once any slot i is identified by code k, step 430 need not continue for a particular code k. Also, a somewhat powerful development of this embodiment would test all 15 slots for each code k, but once the frame timing is determined and step 430 ends for code k, the search time is reduced. The If all 15 slots have been tested and code k is not located, then it is determined that pilot j is not associated with the base station transmitting pilot j and the next code k in step 420 is tested.
[0037]
Step 440 is nested within step 430. In this step, the window surrounding the slot boundary identified by pilot j in step 220 is searched. This search is performed by correlating the code k in each hypothesis of the search window. In general, windows are searched with half-chip increments using correlation techniques known in the art. Each hypothesis is correlated for period N. N may be any time measurement, but a convenient choice is a chip, slot, or frame. By choosing a relatively large value of N, the increased search time tradeoff results in more accurate energy measurements of various hypotheses. Various means for correlating sequences such as code k with incoming I and Q samples are known in the art, and one embodiment operable by the steps shown in FIG. 3 is described in detail below with respect to FIG. Is done. Techniques for using multiple correlators in parallel to reduce search time are also known in the art. It should be noted that the pilot transmitted by the base station is transmitted continuously and the search for code k can store energy from a continuous stream of chips. Thus, for clarity, the example of accumulating N = 2,560 chips, apart from a parallel searcher, requires a period of 2,560 chip times. Conversely, since the PSC is transmitted only on the first 256 chips of each 2,560 chip slot, it takes 25,600 chip hours to accumulate M = 2,560 chips in step 220 Yes. The same 10: 1 frame to slot ratio is retained for the SSC search described above. This is one of the advantages of taking time to search for a pilot code such as code k as compared to taking time to search for an SSC code (a step not required in the present invention). Let's recall. Adding a parallel searcher to this example changes the calculated chip time, but the relative benefits remain the same.
[0038]
The advantages of searching the window around the slot boundary include offset changes due to Doppler or drift, uncertainty about the exact slot timing, and mitigation against multipath signal positioning corresponding to a single base station. . However, an increase in window size results in an increase in search time. This embodiment can be deployed without windowing (ie, a window size of 1) and step 440 becomes a single correlation step. Any window size may be used within the scope of the present invention.
[0039]
Step 440 can end at any time during the window search if the offset is positioned with sufficient energy. The end of the search naturally reduces the search time. Various other termination algorithms will be apparent to those skilled in the art, such as terminating the window search once a predetermined number of multipath signals are positioned above the threshold. Alternatively, the entire window may be searched without determining whether the pilot is positioned. After the window search is complete, a decision on the detection of one or more pilots and associated multipath signals is made using a peak detection and / or classification process with energy calculated from each hypothesis in the window.
[0040]
FIG. 5 shows a flowchart detailing the second step embodiment of the two-step search process 230 described above. The dashed box indicates the portion of the flowchart corresponding to steps 410-440 above. Step 440 includes steps 530 to 544. Step 430 has step 440 and steps 520-524 nested therein. Step 420 has step 430 and steps 510-518 nested therein. Step 410 has step 420 nested within it as well as steps 500-506.
[0041]
The process begins at step 500, where j is set to zero and a pilot loop is started. Proceed to decision block 502 to test whether j is equal to J. If j is equal to J, the loop is complete when each of the J strongest pilots is tested. Proceed to search completion block 504. If j is not equal to J, pilot j must be tested to determine which of the neighbor list codes, if any, corresponds to pilot j. Proceeding to block 510, the nested step 420 is started to test pilot j.
[0042]
At block 510, the code loop is started with k set to zero. Proceed to decision block 512 to determine if k is equal to K. If they are equal, all codes remaining to be tested in the neighbor list have been tested for pilot j. Proceed to decision block 514. In decision block 514, if one or more pilots from the neighbor list have been positioned for pilot j, the pilot and frame timing are determined and proceed to block 506. At block 506, j is de-incremented by 1 and the flow proceeds to block 502 to test if any of the J strongest pilots remain to be tested. In decision block 514, if code k of the tested K codes is not located in pilot j, pilot j is from a base station not shown in the neighbor list. Proceed to block 516 to take appropriate action for the situation as described above. An example is to complete a three-step WCDMA search to determine which code is in pilot j. Subsequently, the code may be reported back to the system and added to the neighbor list. Alternatively, pilot j may be ignored if it is not included in the neighbor list. If appropriate action is taken, proceed to block 506 to increment j and test whether any additional pilots require testing at block 502. If the system is designed to take no action when it is found that pilot j does not correspond to any of the K components of the neighbor list, steps 514 and 516 may be omitted and k is equal to K. The flow from decision block 512 proceeds directly to block 506.
[0043]
At decision block 512, if k is not equal to K, the additional code remains for testing on pilot j. Proceeding to block 520, a nested step 430 is started to test code k. At block 520, i is set to zero to begin the slot loop. As described above, each of the 15 slots must be tested with code k on pilot j until the slots match or all 15 are gone. Proceeding to decision block 522, it is determined whether i is equal to 15. If equal, all 15 slots have been tested and code k is not positioned on pilot j. Proceeding to block 518, k is incremented by one. Proceeding from decision block 512 to block 518, the additional code is tested if needed for pilot j.
[0044]
In decision block 522, if i is not 15, proceed to block 530 to begin nested step 440 to test slot i. At block 530, the window loop is started with w set to -W. In this loop, w represents the window offset, and ranges from -W to W-1. Various windowing schemes will be apparent to those skilled in the art and are within the scope of the present invention. Proceed to decision block 532 to test whether w is equal to W. If so, the window is complete and proceeds to decision block 534. At decision block 534, it is tested whether one or more pilots corresponding to code k in pilot i slot i have been detected. If not, proceed to block 524 to increment i by 1 and proceed to decision block 522 to determine if additional slots remain to be tested.
[0045]
In block 534, if one or more pilots are detected in the window corresponding to code k in pilot j's slot i, the frame timing is only aligned with one of the 15 slots, so optional There is no need to search for additional slots. Thus, the slot loop may be terminated for code k. (A slightly concise and more powerful alternative to this embodiment is to continue searching all slots even if one slot has already been determined to identify frame timing and code. (In general, adopting such an alternative increases the search time and there is no performance gain. This alternative is not shown in FIG. 5.)
Further, one pilot may be received with multiple offsets due to multipath propagation, but only that one pilot is transmitted using code k. In testing on any of the remaining J pilots, there are various techniques to eliminate the need for code k search once positioned. As a result, subsequent search steps may require fewer code searches and the net search time is reduced.
[0046]
If each of the J pilots to be tested comes from a unique base station, code k is positioned for pilot j. There is no need to search for the code k in subsequent pilots. However, it is possible that two or more of the strongest pilots located in step 1 are actually multipath components of a single transmitted pilot signal. If the code k detected in the first such pilot j is not searched in the rest of such pilots, the codes for those remaining multipath pilots are not identified. A time-consuming three-step WCDMA search may be initiated just to see that the pilot corresponds to the code k excluded from the neighbor list. One solution is to remove code k from matters relating only to pilots that are outside the multipath profile of pilot j where code k was first detected (ie, with multipath components of the same transmitted pilot signal). A pilot whose offset is far from pilot j).
[0047]
Another alternative is to size the search window to include the full offset needed to cover the maximum spread spread for the propagation environment. Using this alternative, code k is tested against all possible multipath pilots during one window search. Thus, any of the J pilots remaining to be tested that are actually multipath components of pilot j (and therefore also use code k) are identified during the window search, followed by code k. Excluded from all searches. Further, if code k is positioned at another offset in the search window and that offset corresponds to one of the J pilots remaining to be tested, that pilot is at least one code Is associated with the code k. In this case, the option (not shown in FIG. 5) is to reduce the total search time by removing subsequent pilots from the list and incrementing J by one. This option is used when it is not desirable to retrieve multiple codes corresponding to a single pilot, as described above.
[0048]
In yet another alternative, if code k is not detected at the slot boundary detected in step 1 or in a small window around the boundary (to account for the variance introduced after the search in step 1), the above As such, do not search for larger windows that correspond to multipath profiles. If the first component is detected, it is only necessary to search for additional multipath components. Using such a varying window size provides the flexibility to quickly find all multipath components for code k, thereby adding a heavy load of searching for a larger window for each code / slot hypothesis. Instead, the search time can be reduced by eliminating one or more of the code k and the remaining J pilots. This option is not shown in FIG.
[0049]
Proceed to block 536 to remove code k from the list of K adjacent codes being tested. If the existing scheme is used to maintain a track of K codes, the remaining codes should be shifted down to one. K may then be decremented by one. Since the remaining code is shifted, it is not necessary to increment k, if any, as already indicated in the next code to be tested. Various other loop and index schemes known in the art may be substituted for the exemplary loop of this embodiment. These substitutions are within the scope of the present invention. Here K is smaller than before, and each subsequent use of step 420 is accordingly shortened in terms of search time. If the code is associated with a pilot, the search time for remaining pilots continues to be reduced. (Also, a somewhat simpler and more powerful alternative is to search each code in the test of all subsequent pilots j and keep K unchanged, even if the additional pilot j does not correspond to code k. Using the above technique for dealing with multipath pilots, using such an alternative increases the search time and there is no performance gain, which is not shown in FIG.
As described above, this embodiment may be configured to search for additional codes for the first code k if it is associated with a single pilot. This is illustrated in FIG. 5, where the flow proceeds from step 536 to decision block 512 where, if any, the additional code k is tested with pilot j (the pilot is determined to be associated with the previous code k). ) (Recall that k is not updated because the neighbor list has been edited and K has been decremented. The code k tested in this loop is the end of the list, i.e., k is equal to k-1, the step The decrement of K at 536 makes k equal to K when step 512 is executed, and the loop ends.) The alternative is shown with a dashed line between steps 536 and 506. Once the probability that two codes exist asynchronously in a single pilot j is judged to be very small or the effect of ignoring additional pilots is deemed acceptable, once pilot j is Associated with code k, the pilot loop is terminated and the remainder of the J strongest pilots may be tested. Therefore, the solid line between step 536 and decision block 512 is deleted. When one pilot is detected, there is no need to test the additional code k. Instead, go to block 506. Increment j by 1 to determine if there are any remaining pilots to test and proceed accordingly.
[0050]
If at decision block 532 w is not equal to W, proceed to step 538 to test offset w, slot i, code k, and pilot j. This is done by correlating the incoming I and Q samples with the code k at the offset determined by calculating the offset j + 2560 (i) + w. The offset j is an offset corresponding to the pilot j determined in the first step 220 of the two-step search procedure. Correlation proceeds during period N, which may be any period, but a convenient measure of correlation time is a chip, slot, or frame. Once the correlation for offset w has been calculated, proceed to decision block 540 to determine whether pilot j at code k has been detected. One example is to calculate the received energy and compare it to a threshold value. If a pilot is detected, proceed to step 542 to store this offset in such a way that the associated pilot and code can be identified thereby. Other parameters such as calculated energy may also be stored. After storing in step 542, or if no pilot is detected in decision block 540, proceed to step 544 to increment w by 1 and proceed to decision block 532 where additional offset in the window remains to be tested. Judge whether or not. As described above, in order to position two or more multipath signals, or to compensate for drift, i.e., uncertainty, in the slot timing determined in step 220, even if the received signal is positioned, It would be desirable to search the whole. Alternatively, the window loop may be terminated early if a sufficient number of signals (including only a single signal) are positioned by the received energy. The details of exiting the window loop early are not shown in FIG. 5, but will be apparent to those skilled in the art.
[0051]
An alternative of steps 540 and 542 may be used as follows (details not shown in FIG. 5). Rather than testing the pilot at each offset, the energy of the entire window may be calculated and stored. These energies may then be peak detected and classified (using techniques known in the art or the embodiment shown below in FIG. 7). If so, one or more offsets above the threshold can be used to determine that the code k has been positioned and the associated frame timing. This technique also contributes to the development of correlators that are known in the art and are designed to search windows without intervention, as well as parallel searchers to correlate more than one offset at a time.
[0052]
Yet another alternative for making a pilot detection decision is to combine the energy from multiple detected multipath components corresponding to code k and compare the combined energy to a threshold. If the binding energy exceeds the threshold, the pilot is detected even if the multipath signal component does not exceed the required threshold.
[0053]
FIG. 6 shows an embodiment of the subscriber unit 106 configured for use with the method embodiment as described above. Only a subset of the components of the subscriber unit are shown. A signal is received at antenna 610 and sent to RF downconversion block 620 for amplification, downconversion, and sampling. Various techniques are known in the art for downconverting a CDMA signal to baseband. From the RF down-conversion block 620, I and Q samples are sent to the searcher 630. Searcher 630 is in communication with a digital signal processor (DSP) 640. Alternatives to DSP adoption include using another type of general purpose processor, or specialized hardware that is designed to perform various tasks related to searching, which may be used in the DSP. Depending on the function of searcher 630, DSP 640 performs the various tasks described in the above method and adjusts the performance of the remaining tasks of searcher 630. Although only one searcher 630 is shown in FIG. 6, any number of searchers can be implemented in parallel according to the principles of the present invention. Searcher 630 ultimately sends an energy value corresponding to the offset to DSP 640. The offset may be sent as a classified and detected peak if the function is present in the searcher 630. Alternatively, the initial energy value may be sent for further processing at the DSP.
[0054]
FIG. 7 illustrates an embodiment of the searcher 630. With this embodiment, the PSC search required for step 1 of the two-step search method 220 and the PN search as required for step 2 of the two-step search method 230 can be performed. The I and Q samples are sent to the front end 710 and various procedures such as decimation, code Doppler adjustment, and frequency rotation may be used. The adjusted I and Q samples are sent to the correlator 720. The I and Q sequences are correlated by the sequence sent from the sequence generator 730 to the correlator 720. The sequence can be a PSC sequence that performs step 220 (or associated step 310), or a PN sequence that is associated with code k in step 230 (or associated step 440 or 538). Various correlators are known in the art to despread I and Q samples with the sequence from sequence generator 730 and generate one or many chips of despread I and Q sums per tested offset It is. The result is sent to coherent accumulator 740, where the sum of I and Q from correlator 720 is accumulated separately (thus the accumulation is coherent). For a correlator that generates multiple outputs corresponding to multiple tested offsets, coherent accumulator 740 can generate and store multiple coherent accumulations. Some of the above correlation periods M or N may occur coherently depending on the parameters of the system being used. The coherent I and Q accumulations are then squared in squarer 750 (I ² + Q ² ), Generate an intermediate energy value, and the result is sent to a non-coherent accumulator 760. The non-coherent accumulator 760 accumulates energy values until the correlation period M or N has elapsed, depending on whether step 1 or step 2 is being processed, respectively. Also, for correlators that process multiple offset hypotheses simultaneously, the non-coherent accumulator 760 can store multiple energy accumulations for these hypotheses. The energy values calculated in non-coherent accumulator 760 are then sent to peak detection and classification block 770 where the energy peaks are located and these peaks are classified and energy from highest to lowest depending on their associated offset. Generate a list of These peak / positioning pairs may then be sent to the DSP 640, for example.
[0055]
Various blocks are in communication with the timing control block 780, which provides coherent and non-coherent accumulation sequencing and other controls, if used, required for multiple offset hypothesis testing. . Other searcher embodiments may include a subset of the blocks described with reference to FIG. 7, with remaining tasks performed in the DSP, such as DSP 640 or special purpose hardware as described above. Various configurations of searchers are known in the art, and new searchers can be developed, all of which can be used to generate the results described in the above embodiments, and these Within the scope of the invention.
[0056]
It should be noted that in all the above embodiments, the method steps can be interchanged without departing from the scope of the present invention.
[0057]
Those of skill in the art will understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description are represented by voltage, current, electromagnetic wave, magnetic field or particle, light field or particle, or combinations thereof. May be.
[0058]
Those skilled in the art further appreciate that the various illustrative logic blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein are implemented as electronic hardware, computer software, or a combination of both. You will recognize that you may. To clearly illustrate this interchangeability of hardware and software, various example components, blocks, modules, circuits, and steps have been outlined in terms of their functionality. Whether such functionality is realized by hardware or software depends on the particular application and design constraints imposed on the overall system. The skilled person can implement the functionality described above in a variety of ways for each particular application, but such implementation decisions should not be construed as deviating from the scope of the invention.
[0059]
Various exemplary logic blocks, modules, and circuits described in connection with the embodiments disclosed herein may be general purpose processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable. Realized or implemented by a gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or combinations thereof designed to perform the functions described herein. Good. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. The processor may also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors associated with a DSP core, or other such configuration.
[0060]
The method or algorithm steps described in connection with the embodiments disclosed herein may be implemented directly in hardware, in software modules executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, removable disk, CD-ROM, or other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may be present in the user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.
[0061]
The above description of the disclosed embodiments enables those skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Accordingly, there is no intention to limit the invention to the embodiments shown herein, but to allow for a maximum range consistent with the principles and novel features disclosed herein.
[Brief description of the drawings]
[0062]
FIG. 1 is a schematic block diagram of a wireless communication system capable of supporting a large number of users.
FIG. 2 shows a two-step handoff search method.
FIG. 3 shows a detailed embodiment of the first step of the two-step handoff search method.
FIG. 4 shows a detailed embodiment of the second step of the two-step handoff search method.
FIG. 5 shows an embodiment of the second step of the two-step handoff search method with more detailed sub-steps.
FIG. 6 illustrates an embodiment of a subscriber unit configured in accordance with an exemplary embodiment of the present invention.
FIG. 7 illustrates an embodiment of a searcher configured in accordance with an exemplary embodiment of the present invention.

Claims (20)

Search method, the search method comprises:
Correlating the received signal with a slot timing code to locate one or more associated pilots and slot boundaries;
A received signal is correlated by each in the code list for each of the pilots to identify the pilot code associated with each pilot and the frame timing. , The step of correlating the incoming data stream with a slot timing code further comprises correlating the received signal with the slot timing code for a specific period to calculate received energy corresponding to each slot hypothesis. The method according to 1. The method of claim 2, further comprising the selecting one or more slot hypotheses having maximum received energy as the one or more positioned pilots. The method of claim 2, wherein the slot code is a primary synchronization code (PSC). The method of claim 1, wherein the code list is a neighbor list received from a base station. The method of claim 1, wherein correlating the received signal with the code list comprises:
A pilot test is performed for each pilot, the pilot test comprising:
Performing a code test for each code in the code list, the code test comprising:
Performing a slot test for each slot corresponding to the pilot, the slot test comprising correlating the received signal with the code over a period at an offset corresponding to the slot to generate an energy value . The method of claim 6, further comprising comparing each energy value to a threshold to determine whether the code corresponds to the pilot. Further, the code corresponding to the energy exceeding the threshold is used as a scrambling code for demodulation, and the slot boundary corresponding to the energy exceeding the threshold is used as the scrambling code. Using the method as a frame boundary. The slot test further includes
7. The method of claim 6, comprising testing a window of offset hypotheses around the slot boundary, wherein for each offset hypothesis, the received signal is correlated by the code for a period of time to generate an energy value. the method of. The method of claim 9, further comprising peak detecting the energy value corresponding to the offset hypothesis to locate one or more peaks. The method of claim 10, further comprising comparing each of the peaks to a threshold to determine whether the code corresponds to the pilot. Further, for each peak exceeding the threshold, use the corresponding code as a demodulation scrambling code;
The method of claim 11, comprising using the corresponding slot boundary as the frame boundary for the scrambling code for each peak that exceeds the threshold. 12. The method of claim 11, further comprising terminating the step of testing an offset hypothesis window around the slot if a predetermined number of peaks are detected above the threshold. The method of claim 11, further comprising terminating the code test for the pilot if one or more peaks are detected above the threshold during the slot test. The method of claim 11, further comprising terminating the pilot test of a pilot if one or more peaks are detected above the threshold during the code test. 12. The method of claim 11, further comprising deleting the code from the code list for subsequent pilot testing if one or more peaks are detected above the threshold during the code test. . A first correlator for correlating the received signal with a slot timing code to locate one or more pilots and slot boundaries associated therewith;
A hand-off searcher comprising: a second correlator for correlating the received signal with a code list for each of each pilot to identify the pilot code and frame timing associated with each pilot. The searcher of claim 17, wherein the first correlator and the second correlator are the same correlator. A subscriber unit for use in a CDMA system, including a searcher for handoff retrieval, the subscriber unit comprising:
Correlation means for correlating the received signal with a slot timing code to locate one or more associated pilots and slot boundaries;
Correlation means for correlating the received signal with each of the code lists for each of the pilots to identify the pilot code and the frame timing associated with each pilot. W-CDMA system including a searcher for handoff search, the W-CDMA system comprises:
Correlation means for correlating the received signal with a slot timing code to locate one or more associated pilots and slot boundaries;
Correlation means for correlating the received signal with each of the code lists for each of the pilots to identify the pilot code and the frame timing associated with each pilot.

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